An anode material of a lithium secondary battery capable of implementing high capacity and power is required to be used for a battery for an information technology (IT) equipment or a battery for an automobile. Accordingly, silicon has attracted attention as the anode material of the lithium secondary battery with high capacity. For example, it is known that pure silicon has a high theoretical capacity of 4200 mAh/g.
However, as compared with a carbon-based material, silicon has deteriorated cycle property, which is still an obstacle to practical use. The reason is because when inorganic particles such as silicon, as an anode active material, are directly used as a material for absorption and release of lithium, conductivity between active materials is deteriorated due to a change in volume during a charge and discharge process, or the anode active material is separated from an anode current collector. That is, the inorganic particles such as silicon included in the anode active material absorb lithium by a charge process to expand so as to be about 300% to 400% in volume. In addition, when the lithium is released by a discharge process, the inorganic particles are contracted, and when the charge and discharge cycles are repeated, electrical insulation may occur due to empty space generated between the inorganic particles and the anode active material to cause rapid deterioration in cycle life, and therefore, the inorganic particles have a serious problem in being used for a secondary battery.
Further, as a value obtained by dividing an amount of lithium releasing during a discharge process by an amount of lithium absorbing during an initial charge process becomes higher, an amount of a cathode consumed when an initial charge and discharge cycle proceeds becomes smaller, which is advantages in view of an initial efficiency. However, the existing silicon-based anode active material has a problem of low initial efficiency.
In addition, a secondary battery for an automobile requires high power capable of maintaining capacity even under harsh charge and discharge condition. However, there are many cases in which the existing graphite-based anode active materials and silicon-based anode active materials do not exhibit high power under harsh condition.